Abrasive blasting



y 1946. ,w. L. KEEEER 2,399,680

ABRAS I-VE BLAST ING Filed April 12, 1945 Patented May 7, 1946 UNITED STATES OFFICE ABRASWE BEASTING I Walter L..Keef'er, Hagerstown,.Md'-.,.assignor to Pangborn Corporation, Hagerstown, Md, a corporation of Maryland I Application April 12, 1945; Serial-'No. 587,874

' (or 5I-'-282) 4 Claims.

The present invention relates to a method of propelling abrasive particles at blasting velocities whereinthe granular abrasive material is accelerated by: expanding gasesresulting" from the deflagration of 'solid combustible materials.

It is. an object of the invention to provide a method for accelerating abrasiveto a-velocity for blasting articles, abrading various materials or peening' articles, by a gaseous mediumpl'aced under pressure during the deflagration of suitable combustible materials and permitting'the' gaseous medium to expand as a forceful jet which is utilized to carry the abrasive particles forwardly into impingement with the articleor'surface'to be treated by bombardment of the abrasive particles.

These objects and othercharacteristic features of the invention will be more clearly understood and appreciated as the present disclosure proceeds-and upon'considerationof the accompanying drawing wherein an exemplary type of apparatus is diagrammatically illustrated for carrying out the invention.

This invention relates to the propulsion of granular abrasive material by means of an expanding gaseous medium so as to carry the abrasive particles forwardly as a blast stream for cleaningarticles', cutting or abrading the surface or peening articles to increase the fatigue life thereof. In carrying outthe invention a suitable combustible material is deflagrated within a confined space or chamber whereby gas pressure gengenerated'in the chamber [5 to pass into the tank I2 but preventsthereturn of'the gaseous medium into the housing It; The storage tank l2 may be encasedwith-suitable insulating material It to prevent the coolingof thegases stored therein and a reduction of pressure within the tank It. The housing 1- may be provided with a plug is threaded in an opening in the lower portion thereof whereby any residue may be removed fromthis housing;

The gaseous medium stored in the tank l2 may be supplied to a. blast gun 22 of'a conventional type through a hose 24 when the valve .26 is open; The blast gun 22 is of the type which is adapted to provide a partial vacuum therein as the gaseous medium passes therethrough. The abrasive particles may be stored in a hopper- 28 and drawn into the gun 22 through a hose 32 whereby the abrasive particles are entrained in theforceful jet escaping from the-gun 22. The abrasive particles entrained in the expanding gaseous medium may therefore be moved into engagement with the surface or article to be treated andwhich is diagrammatically represented at 34.

The combustible material for defiagration within thehousing lll-isin the form of a rope or cord 38; A coilof the rope or cord is. shown at 3'8.

' This cord may have an outer sheathing or jacket erated during such burning provides a gaseous medium under increased pressure which then moves into a storage tank. A supply of gaseous medium under pressure is thus obtained which is utilized for propelling the abrasive. The gaseous medium under pressure is permitted to move from the storage tank and expand through a nozzle or gun to provide a forceful jet of the expanding gaseous medium in which the abrasive particles are entrained and moved at blasting velocities into engagement with the article or surface to be blast treated.

One type of apparatus for carrying out the invention is shown in the drawing. A housing II] is provided within which combustible material as hereinafter described is to be deflagrated for the generation of a gaseous pressure therein. The housing Ill provides a chamber l5 therein which is completely closed so that upon deflagration of the combustible material a gaseous pressure is built up within the housing. The chamber I5 is connected to a storage tank 12 by means of a conduit l6. A check valve M is arranged in the conduit l6 which permits the gaseous pressure formed of helically wound ribbon with the edges of the ribbon overlapping and forming a continuous tube within which the combustible material is arranged. The rope or cord 38 is fed into the housing H! by means of a plurality of rollers 4| which may be driven at a speed to feed the rope or cord into the housing Ill at a rate substantially equal to the speed at which the combustible material is deflagrated. The housing I0 is accordingly provided with an apertured extension 31 and a heat insulating bushing through which the rope like combustible material is fed into the combustion chamber l5. The rope or cord may be ignited by any suitable mean such as an electrically heated device 42 which carries a hot wire element adjacent the point where the rope like combustible material enters the combustion chamber. It will be appreciated that after the combustible material has been ignited the igniting device may be rendered inoperative until it is desired to re-establish combustion within the housing I0. As the supply of the cord or rope 38 is being exhausted the end of another rope may be introduced between the rollers M so as to provide a continuous generation or the gaseous pressure within the combustion chamber l5.

The cord or rope may contain a mixture of potassium nitrate, sulphur and charcoal within the helically wound ribbon which provides a sheath for the combustible material. Such a mixture is known as black gun powder and upon deflagration thereof within the combustion chamber I5 provides for the generation of a gaseous medium under relatively highpressure. The combustible material may also comprise-a nitrocellulose base propellant material. Thus the nitrocellulose material may be colloided with a solvent such as alcohol-ether, acetone or ethyl acetate. The colloided material preferably-retains part of the solvent so as to reduce the burning rate. Accordingly, a non-volatile solvent may be employed such as ethyl ether or ethylene glycol. Other solvents that may be employed include methyl ether of ethylene glycol, glycol diacetate, monoethyl ether of diethylene glycol and all of these solvents may be regarded as low molecular ethers andesters of ethylene glycol.

The present invention provides a method of abrasive blasting wherein the combustible material may be continuously burned to provide a sup ply of gas under pressure within the tank l2.

The defiagration of the combustible rope or cord .38 generates a gaseous pressure within ,the chamber which escapes through the check valve Hi into the tank l2. The pressure increase in the chamber I5 is to some extent obtained from the increase in temperature attendant the burning of the combustible material and the gaseous medium in the tank I2 is maintained at an elevated temperature by the insulating jacket I 2. When it is desired to initiate a blasting operation the valve 28 is opened whereby the gaseous medium under pressure moves from the tank [2 through the hose 24 and the gun 22. The rush of the propellingmedium through the gun or nozzle creates a vacuum therein for drawing abrasive through the hose 32 into the gun. The abrasive is entrained in the propelling medium and is moved forwardly by the forceful jet and into engagement with the article or surface to be blasted,

While the invention has been described by reference to, particular apparatus and'to specific types of materials for the generation of the gaseous pressure it is apparent that changes may be made in the apparatus and the character of the explosive materials. Such changes may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. A method of propelling abrasive particles at blastingvelocities which comprises, defiagrating a combustible material in a confined space to provide a gaseous medium under pressure,

' storing the gaseous medium under pressure, permitting the gaseous medium to expand as a forceful jet, and entraining abrasive particles in the jet whereby the abrasive is moved forwardly as a blast stream,

' 2. A method of propelling abrasive particles as a blast stream which comprises, defiagrating an explosive material in a confined space to generate a gaseous pressure for escape into a storage chamber, continuing the defiagration of the explosive material, permitting the gas to expand from the storage chamber as a forceful jet, and entraining abrasive particles in the forceful jet to provide a high. velocity blast stream.

3. A method of abrasive blasting which comprises, defiagrating a combustible material in a confined chamber to increase the gaseous pressure therein, moving combustible material into the chamber at a speed substantially equal to the burning rate to provide recurring pressure increases in said chamber, permitting gaseous medium to expand as a forceful jet in the presence of abrasive particles to provide an abrasive blast stream.

4. A method of abrasive blasting which comprises, moving a cord shaped combustible material into a closed housing, igniting the combustible material within the housing to increase the pressure therein and moving the combustible material into the housing at, a speed corresponding substantially to the burning rate of the material, and employing the gases expanding from said housing to entrain and-move abrasive particles as a forceful abrasive blast stream.

. WALTER- L. KEEFER. 

